Detective Donald I

Detective Donald investigated the scene of the crime. Apparently, the fifth richest man in Crimeville, Bill Richman, had been kidnapped! The only thing at the scene was a note left, no doubt, by Bill Richman while he was being kidnapped. It read, "First of January, Fourth of October, Fifth of March, and Third of June." Detective Donald knew this note was accusing the kidnapper. He had to decide which one it was, out of:
Jack Richman, Bill Richman's son and heir,
John Jacobson, Richman's employee, or
June Richman, Bill's wife.
Detective Donald discovered what the note meant, and promptly told the authorities who it was.